While fractional dosing greatly extends the supply of available vaccine, the downside is recipients would be unlikely to gain lifetime immunity (more likely 12 months or so), and would not receive a standard yellow fever vaccination certificate.

The decision announced on June 17th was described as an emergency fall-back plan, with the WHO stating the situation didn't currently call
for its implementation, but if the situation in Africa worsened
substantially . . . .

Fast forward a little over a week and the Health Minister of the DRC has announced plans to vaccinate the entire population (over the age of 9 mos) of the capital - Kinshasa - and target populations in Kwango, Lualaba and Kasai provinces.

With reportedly only 1.6 million doses of vaccine available in the DRC - even if diluted to 1/5th strength - it isn't clear how they will obtain enough vaccine to provide the estimated 11.6 million doses required.

Brazzaville, 22 June 2016 –
As the yellow fever outbreak in Angola and Democratic Republic of the
Congo continues, the World Health Organization will launch emergency
pre-emptive vaccination campaigns on the DR Congo, Angola border and the
city of Kinshasa in the DR Congo to halt the epidemic and prevent the
risk of further international spread.

The
initial phase of the campaign which begins in July will focus on
districts where there is high movement of people and intense trade
activities, particularly the northern border districts of Angola and
targeted border districts in neighbouring countries. Specifically,
within a 75-100km belt spanning the border between Angola and DR Congo
and targeted health zones/communes at risk in Kinshasa city in the DR
Congo. This will create an immune buffer to prevent further
international spread.

So far, I haven't seen any official comment from the WHO on the DRC's more aggressive plan. The most complete coverage of the DRC's decision comes from VOA NEWS.

The Democratic Republic of Congo says it will begin a campaign next month to vaccinate 11.6 million people against yellow fever after an epidemic was declared in the capital.

Health Minister Felix Kabange said the campaign will begin July 20 and will aim to vaccinate everyone in the capital of Kinshasa except children under nine months, and will also target populations in the provinces of Kwango, Lualaba and Kasai.

Last week, Congo's government announced an epidemic in Kinshasa and two other provinces after reporting 67 confirmed cases of yellow fever and more than 1,000 other suspected cases. An outbreak in neighboring Angola has led to the deaths of about 345 people.

Kabange did not say how health authorities would acquire enough vaccination doses for the campaign. The vaccine is in short supply around the world, and takes about a year to make.

The World Health Organization recommended this month that the vaccine be diluted up to a fifth of the standard dose to deal with the current emergency.

The WHO says the lower dosage will protect people for at least a year, but will likely not give lifelong immunity.